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Produced by the NASA Center for Aerospace Information (CASI) 26 J76-26129 (NASA-!; ,0 -14}? 17 ti ) T»iT l't )ISCIPLIhAi>Y g S i1i COAPAkATIVF PLANETUL66Y Ir4VF^Ti t AT 141 ANNUAL :iTATUS kt.P ts'T, 1 JtPI. 1975 - 3J JtJL. 19 P Hf, g 3.^J CSl`.L J33 G3/91 UNC(.AS 1971 (C kRNELL 11NIV.) 42e37 CORNELL UNIVERSITY Center foa^ 1Zadiophysics and S'pace Research TT,, ITHACA, N. YY CRSR 636 ANNUAL STATUS REPORT to the NATIONAL AERONAUTICS AND SPACE ADMINISTRATION under NASA Grant NGR 33-010-220 INTERDISCIPLINARY INVESTIGATIONS ^O P COMPARATIVE PLANETOLOGY July 1, 1 ,975 through June 30, 1976 ^^212a2^-, JUN 1976 Principal Investigator: Prof. Carl Sagan RECE'Vca - i _1 a TABLE OF CONTENTS A. Martian Channels . 1 B. Variable Features on Mars . 2 C. The Surfaces and Origins of the Martian Satellites . 7 D. The Surface of Venus . 11 E. Miscellaneous . • . 14 k The following are abstracts q f paper., published within the last vear (or in press) on scientific results supported wholly or in part by the Planetolof,y Programs Office, NASA Headquarters and written by personnel of the Laboratory for Planetary Studies: A. MARTIAN CHANNELS (1) Distribution of Small Channels on the Martian Surface. Icarus 27, 25-50 (1976). The distribution of small channels on Mars has been mapped from Mariner 9 images, at thA 1:5 000 000 scale, by the author. The small channels referred to here are small valleys ranging in width from the resolution limit of the Mariner 9 wide-angle images (ti 1 km) to about 10 km. The greatest density of small channels occurs in dark cratered terrain. This dark zone forms a broad sub- equatorial band around the planet. The observed distribu- tion may be the result of decreased small-channel visibility in bright areas due to obscuration by a high-albedo dust or sediment mantle. Crater densities within two small- channel segments show crater size-frequency distributions consistent with those of the oldest of the heavily cratered plains units. Such crater densities coupled with the almost exclusive occurrence of small channels in old cratered terrain and the generally degraded appearance of small channels in the high-resolution images (ti 100 m) imply a major episode of small-channel formation early in Martian geologic history. 1 P (2) A Comment on the Paper by Florenski et al., Icaruo 26, 230 (1975). The nature of Nirgal Vallis may compromise the findings of Florenski et al.; comprehensive image references would enhance the analysis. B. VARIABLE FEATURES ON MARS (3) A Numerical Circulation Model with Topography for the Martian Southern Hemisphere. Journal of the Atmospheric Sciences, in press. A quasi-geostrophic numerical model, including friction, radiation, and the observed planetary topography, is applied to the general circulation of the Martian atmosphere in the southern hemisphere at latitudes south of about 35 0 . Near equilibrium weather systems developed after about 5 model days. To avoid violating the quasi-geostrophic approximation, only 0.8 of the already smoothed relief was employed. Weather systems and velocity fields are strikingly tied to topography. A 2mb middle latitude ,jet stream is found of remarkably terrestrial aspect. Highest surface velocities, both horizontal and vertical, are predicted in western Hellas Planitia and eastern Argyre Planitia, which are common sites of origin of major Martian dust storms. Mean horizontal velocities > 3 0 m/s and mean vertical velocities < 0.2 m/s are found ,just above the surface velocity boundary layer, apart from eddy velocity contributions. When consideration f 3 is taken of scaling to full topography and the probable gustiness of Martian winds, it seems very likely that the general circulation is adequate, at certain times and places, to transport dust from the surface of Mars, as observed. Certain sources and sinks of vertical dust streaming are suggested; the entire south circumpolar zone appears to be a dust F31nx in winter. (4) Fluid Transport on Earth and Aeolian Transport on Mars. Icarus 26, 209-218 (1975). Experimental data on cohesion-free particle transport in fluid beds are applied, via a universal scaling relation, to atmospheric transport of fine grains on Mars. It may be that cohesion due to impact vitrification, vacuum sinter- ing, and adsorbed thin films of water are absent on Mars-- in which case the curve of threshold velocity versus grain size may show no turnup to small particle size, and one micron diameter grains may be injected directly by saltation into the Martian atmosphere more readily than 100 micron diameter grains. Curves for threshold and terminal velocities are presented for the full range of Martian pressures and temperatures. Suspension of fine grains is significantly easier at low temperatures and high pressures; late after- noon brightenings of many areas of Mars, and the generation of dust storms in such deep basins as Hellas, may be due to this effect. I i ` I }f (5) Physical Properties of Suspended Aero:.olo from their Infrared Spectra: Application to the Martian Duct Storm of 1971. Icarus, submitted for publication. Infrared spectra of Mars obtained from the Mariner 9 spacecraft during the Martian dust storm of 1971 were analyzed to determine the chemical composition and size distribution of the suspended dust grains. The infrared optical constants of granite and mont-morillonite were measured for the analysis which employs a new, approximate, technique for calculating the emergent intensity from a scattering, emitting dust cloud. The results show that the dust was composed of an intermediate or acidic igneous rock or a weathering product such as a clay. The clay mineral montmorillonite was not the only component of the dust, but the results do not exclude (or require) mont- morillonite as a component of a possible mixture. The dust could not have been composed of a basic igneous rock like basalt, nor could basalt have played a dominant role as a component of a mixture. The mean dust particle radius was a few microns, the dust size distribution closely resembled terrestrial dust size distributions in regions remote from a dust source, and the Martian dust size dis- tribution did not change significantly during the dust storm dissipation. The composition and size distribution of Martian dust have a number of geological and meteorologic implications for Mars. We have also studied the way optical l _ properties of dust interact to create infrared spectra. The transmission spectrum maximum (Christiansen frequency) is not compositionally si gnificant for dust particle:, in the size distributions we studied. Many optical properties interact to create transmission spectra of dust powders and we show that powder transmission spectra cannot be used to obtain infrared optical constants. (6) Variable Features on Mars.V: Evidence for Crater Streaks Produced by Wind Erosion. Icarus 25, 595-601 (1975). Evidence is presented to show that the ragged dark streaks which appeared behind many Martian craters severa' months after the end of the 1971 g lobal duststorm were produced by wind erosion of a thin surface veneer of dust- storm fallout. (7) Variable Features on Mars. VI. An Unusual Crater Streak in Mesogaea. I carus 27, 241-253 (1976). An unusual, prominent dark streak located in Mesogaea (near 8 0 N, 191 °W) is described. Its appearance is unlike that of most dark streaks on Mars, many of which have ragged outlines, are variable on short time-scales, and are pre- sumed to be erosional. The Mesogaea streak has a tapered, smooth outline, and no changes within it were observed. We suggest that this streak is depositional and that the low-albedo material originated within the associated crater itself. The source area is identified with a compact, _ I ,. l 6 low-albedo region on the crater floor. Two possible origins for the dark material are suggested: (1) deflation from a recently exposed, relatively unconsolidated sub- surface deposit, and (2) production of ash by a volcanic vent. (8) Variable Features on Mars. VII. Dark Filamentary Mar:..ngs on Mars. Icarus, in press. Some Mariner 9 B-frames show networks of Criss-crossing rectilinear albedo markings typically 10 km long by 100 meters wide. This paper discusses the location, variability and possible nature of these dark filamentary markings. Although not common on Mars, the markings are concentrated in at least two areas: Depressio Hellespontica and Cerberus/ Trivium Charontis. For Depressio Hellesponviea their emergence coincided with a general darkening of the region which occurred 3 months after the end of the 1971 global duststorm. The very definite crass-cross pattern of many of these markings suggests that they may be controlled by ,joints. It is unlikely that the markings are linear dunes. (9) Variable Features on Mars. VIII. Pandorae Fretum. Icarus, to be submitted. During the Mariner 9 mission a region near (343°W, 24 0 S) was monitored for changes over a period of 5 months (25 Jan to 30 June, 1972).